1. Field of the Invention
The present invention relates to a structure for lubricating a cam sliding surface in an internal combustion engine.
2. Description of Background Art
In a valve system using a push rod in a prior art overhead-valve internal combustion engine, for lubricating a sliding surface between a tappet positioned at the lower portion of a push rod and a cam, a hole is opened in the lower peripheral wall of a cylindrical and bottoming tappet with a top portion opened, so that lubricating oil after lubricating a rocker shaft and rocker arm of a cylinder head is dropped and reserved in the cylindrical and bottoming tappet, and is discharged from the above hole (Unexamined Japanese Utility Model Publication Nos. SHO 57-142112 and SHO 59-96315).
Since a tappet is made of a hard material excellent in wear resistance for withstanding the friction with a cam, it is difficult to be formed with a hole. Moreover, the lubricating oil discharged from the hole of the tappet is not wholly supplied to the sliding surface. Accordingly various structures must be adopted for sufficiently lubricating the sliding surface.